1. Field of the Invention
The present invention relates to an inkjet recording apparatus, and more particularly, to ink supply technology which enables highly accurate control of back pressure even in the case of ink of high viscosity and large flow volume.
2. Description of the Related Art
Conventionally, an inkjet recording apparatus is known which comprises an inkjet type of recording head having a plurality of nozzles and which records a desired image on a recording medium by ejecting ink droplets respectively from the nozzles in accordance with input image data. The ink ejection method may be a piezoelectric method in which ink droplets are ejected from nozzles by utilizing the displacement of piezoelectric elements to pressurize the ink inside pressure chambers, or a thermal method in which ink droplets are ejected from nozzles due to the pressure created by the growth of gas bubbles which are generated inside pressure chambers by means of the thermal energy created by heating elements, such as heaters, or the like. Recording apparatuses of this kind are used in a wide range of fields from commercial to industrial applications, due to their low operating noise, low running costs, and their capacity to record images of high quality onto recording media of many various types.
When the ink contains air bubbles, the pressure applied to the ink inside the pressure chamber is absorbed by the air bubbles which have compressive properties, and the ink droplet ejection performance declines. One of the reasons for the occurrence of these air bubbles is the presence of dissolved gas in the ink. The phenomenon whereby dissolved gas contained in ink is converted into gas bubbles by the high-frequency vibrations generated by the pressure generating device is known as “cavitation”. Therefore, it is necessary to remove dissolved gas from the ink supplied to the recording head, and various technologies for removing dissolved gas from the ink have been proposed hitherto. For example, Japanese Patent Application Publication No. 2007-130907 discloses an inkjet recording apparatus comprising a heating mechanism which heats the ink in an ink supply channel between an ink storage unit which stores ink and a deaeration apparatus, in order to resolve the problem of ejection defects caused by the occurrence of ink supply deficiencies depending on the rate of consumption of the ink. According to this recording apparatus, it is possible to introduce ink into the deaeration apparatus in a state of lowered ink viscosity, and hence the pressure loss can be reduced.
Furthermore, Japanese Patent Application Publication No. 2005-280246 discloses an inkjet recording apparatus (inkjet printer) in which, in order to reduce pressure loss in the pressure loss portion of an ink supply section (for example, filters, or the like) and to ensure stable ink supply even if there is a change in print duty, a flow rate adjustment device is provided to control the flow rate of the ink passing through the pressure loss portion of the ink supply path so as to assume a prescribed flow rate, in accordance with the print duty. According to this recording apparatus, the flow rate of the ink passing through the pressure loss portion is controlled by adjusting the temperature of the ink and thereby adjusting the viscosity of the ink.
However, the inkjet recording apparatus described in Japanese Patent Application Publication No. 2007-130907 has problems in that the pressure loss increases as the volume of ink flowing per unit time through the deaeration apparatus becomes greater (in other words, in cases of large flow rate). Furthermore, since the temperature of the ink is not constant over time, then there is a possibility that the ejection properties decline. Moreover, if the pressure loss in the deaeration apparatus becomes large, then a blocked state occurs in the deaeration apparatus and there are also concerns about the difficulty in maintaining the back pressure of the recording head.
Furthermore, the inkjet recording apparatus described in Japanese Patent Application Publication No. 2005-280246 has a problem in that ejection stability is poor due to change in the temperature of the ink with the print duty. Moreover, it is also necessary to provide a mechanism for implementing control in accordance with the print duty, and this can also lead to increased costs.